Arc-transitive distance-regular covers of cliques with <Emphasis Type="Italic">λ</Emphasis> = µ

We study antipodal distance-regular graphs of diameter 3 such that their automorphism group acts transitively on the set of pairs (a, b), where {a, b} is an edge of the graph. Since the automorphism group of such graphs acts 2-transitively on the set of antipodal classes, the classification of 2-transitive permutation groups can be used. We classify arc-transitive distance-regular graphs of diameter 3 in which any two vertices at distance at most two have exactly µ common neighbors.     

Temperature and concentration dependences of the electrical resistivity for alloys of plutonium with americium under normal conditions

The temperature and concentration dependences of the electrical resistivity for alloys of americium with plutonium are analyzed in terms of the multiband conductivity model for binary disordered substitution-type alloys. For the case of high temperatures (T > Θ_D, Θ_D is the Debye temperature), a system of self-consistent equations of the coherent potential approximation has been derived for the scattering of conduction electrons by impurities and phonons without any constraints on the interaction intensity. The definitions of the shift and broadening operator for a single-electron level are used to show qualitatively and quantitatively that the pattern of the temperature dependence of the electrical resistivity for alloys is determined by the balance between the coherent and incoherent contributions to the electron-phonon scattering and that the interference conduction electron scattering mechanism can be the main cause of the negative temperature coefficient of resistivity observed in some alloys involving actinides. It is shown that the great values of the observed resistivity may be attributable to interband transitions of charge carriers and renormalization of their effective mass through strong s-d band hybridization. The concentration and temperature dependences of the resistivity for alloys of plutonium and americium calculated in terms of the derived conductivity model are compared with the available experimental data.     

Temperature and concentration dependences of the plutonium-americium alloy resistivity at high temperatures

A many-band model of conductivity is stated in terms of which it is shown qualitatively and quantitatively that interference scattering of conduction electrons may be the main reason for the negative temperature coefficient of resistance in actinide alloys at high temperatures (T > Θ_D). The temperature run of the resistivity in such alloys is completely determined by the balance between coherent and incoherent contributions to electron-impurity-phonon scattering. The model is used to analyze the concentration and temperature dependences of the plutonium and americium alloy resistivity.     

On the Automorphism Group of an Antipodal Tight Graph of Diameter 4 with Parameters (5, 7, r)

Mathematical Notes - It is proved that the automorphism group of every AT4(5, 7, r)-graph acts intransitively on the set of its arcs. Moreover, it is established that the automorphism group of any...     

On automorphisms of a distance-regular graph with intersection array {35, 32, 1; 1, 4, 35}

Prime divisors of orders of automorphisms and their fixed-point subgraphs are studied for a hypothetical distance-regular graph with intersection array {35, 32, 1; 1, 4, 35}. It is shown that there are no arc-transitive distance-regular graphs with intersection array {35, 32, 1; 1, 4, 35}.